The invention is directed to a method of manufacturing printed circuit boards in additive technology.
In constructing printed circuits or printed circuit boards, a fundamental distinction is made between the wide-spread subtractive technology which removes copper not required for conductor tracks by etching and the additive technology which metal-laminated substrates or base materials only applies conductor material from baths where the conductor tracks are required on substrates coated with adhesion promoters. Combinations of these methods are also standard. For example, additive methods are used in the interlayer connection, i.e. copper coating of the wall of a hole in the conductor patterns produced subtractively and which are present on both sides of the substrate. In semi-additive technology, the interconnects are constructed by galvanic reinforcement on thin base layers deposited in a currentless fashion and the remainder of the base layer is in turn removed by etching, i.e. subtractively (cf, AEG-Telefunken Handbuecher, Volume 22, "Kunststoffe in der Elektrotechnik" 1979, page 36).
Transferring the conductor pattern with the use of a laser in the manufacture of printed circuit boards in fully additive technology is known from the German periodical "Galvanotechnik" 77, (1986), Number 1, pages 51 through 60. The following transfer mechanisms were considered and investigated:
Direct excitation of the substrate surface or of an adhesion promoter with the laser beam; PA0 Thermic or photochemical excitation or deactivation of an activator layer with the laser beam; PA0 Initiation and acceleration of the metal deposition without external current or of the electro-deposition with the thermal energy of the laser beam.
Of the transfer mechanisms investigated, a Cr (III) layer activation system seemed most suitable for further optimization.